The use of high velocity, abrasive-laden liquid jets to precisely cut a variety of materials is well known. Briefly, a high velocity liquid jet is first formed by compressing the liquid to an operating pressure of 3,500 to 150,000 psi, and forcing the compressed liquid through an orifice having a diameter approximating that of a human hair; namely, 0.003-0.040 inches. The resulting highly coherent jet is discharged from the orifice at a velocity which approaches or exceeds the speed of sound. The liquid most frequently used to from the jet is water, and the high velocity jet described hereinafter may accordingly be identified as a waterjet. Those skilled in the art will recognize, however, that numerous other liquids can be used without departing from the scope of the invention, and the recitation of the jet as comprising water should not be interpreted as a limitation.
To enhance the cutting power of the liquid jet, abrasive materials have been added to the jet stream to produce an abrasive-laden waterjet, typically called an xe2x80x9cabrasive jetxe2x80x9d. The abrasive jet is used to effectively cut a wide variety of materials from exceptionally hard materials (such as tool steel, aluminum, cast iron armor plate, certain ceramics and bullet-proof glass) to soft materials (such as lead). Typical abrasive materials include garnet, silica, and aluminum oxide having grit sizes of #36 through #200.
To produce the abrasive-laden waterjet, the waterjet passes through a xe2x80x9cmixing regionxe2x80x9d wherein a quantity of abrasive is entrained into the jet by the low pressure region which surrounds the flowing liquid in accordance with the Venturi effect. The abrasive, which is under atmospheric pressure in an external hopper, is drawn into the mixing region by the by the lower pressure region via a conduit that communicates with the interior of the hopper. In operation, quantities of up to 6 lbs./min of abrasive material have been found to produce a suitable abrasive jet.
The resulting abrasive-laden waterjet is then discharged against a workpiece through an abrasivejet nozzle that is supported closely adjacent the workpiece.
The material defining the waterjet-forming orifice is typically a hard jewel such sapphire, ruby or diamond. Typical abrasive materials include garnet, silica, and aluminum oxide having grade sizes of #36 through #120. Those skilled in the art recognize that the abrasive material represents the highest hourly operating cost associated with abrasivejet cutting.
Because the waterjet and abrasivejet are so destructive, wear of the jet-forming components is of particular concern. As the jet-forming orifice, mixing region and abrasivejet nozzle become worn, cutting efficiency decreases dramatically. The result is that the cutting process is dramatically slowed, and an excess of abrasive material is consumed in performing the cutting operation. Thus it is necessary to regularly change the jet-forming orifice, the mixing chamber and the abrasivejet nozzle.
To maximize the life of the mixing region and abrasivejet nozzle, it is highly desirable to align them with the waterjet""s axis. Because the fluid path thorough jet housing is several inches long, very minute alignment errors (e.g., a few tenths of a thousandths inch) are enough to cause premature failure of the abrasive jet nozzle.
One disclosed technique for resolving the alignment problem associated with abrasivejet assemblies is disclosed in U.S. Pat. No. 4,817,874 wherein an abrasive jet nozzle is pivotably movable into alignment with the waterjet-forming orifice.
A second technique is disclosed in U.S. Pat. No. 5,144,766 wherein an integral cartridge with the jet-forming orifice, mixing region and abrasivejet nozzle is disclosed.
Briefly, the invention herein is an abrasivejet cutting head assembly for use in an abrasivejet cutting system of the type wherein the cutting head is coupled to a source of abrasive via an abrasive-carrying conduit, and to a source of high pressure water. The abrasivejet cutting head herein is an assembly that comprises a housing having a body disposed about a longitudinal axis between upstream and downstream ends, a first longitudinally-extending passageway in communication with said ends, and a conduit-accommodating passageway extending generally radially from the exterior of the body into a region in the longitudinal passageway. The body is adapted to be coupled to a source of high pressure liquid at its upstream end, and to be coupled to an abrasivejet nozzle at its downstream end.
The assembly includes a removable novel insert member within the first longitudinally-extending passageway, which has upstream and downstream faces, a second longitudinally-extending fluid passageway in communication with said faces and in axial alignment with the first longitudinal passageway, and a radially-extending passage that is aligned with the conduit-accommodating passageway of the housing to place an accommodated conduit in fluid communication with the second longitudinally extending passageway adjacent a mixing region within the insert. The insert member is securable against movement within the housing by the insertion of the sleeve of the abrasive-carrying conduit into its radially-extending passageway
An orifice member is supported within the insert member upstream from the mixing region, and has a waterjet-forming orifice in axial alignment with the second longitudinally-extending passageway. Means are included for securing an abrasivejet nozzle into the downstream end of the housing so that the nozzle is in substantial axial alignment with the second longitudinal passageway.
Additional details concerning the invention will be apparent to those of ordinary skill in the art from the following description of the preferred embodiment, of which the Drawing forms a part.